Catheter: A nurse slides a thin, flexible tube called a catheter through your urethra (where pee comes out) and into your bladder, then takes out the urine.

Ultrasound: A machine uses sound waves to show live images of your bladder so your doctor can see how much urine is there.

Some researchers think catheters measure urine in the bladder better than an ultrasound, while others think the two tests work equally well.

Catheter

A nurse will ask you to pee right before the test. Then they’ll give you medicine to numb the area. They’ll slide the catheter through your urethra, take out the urine in your bladder, and measure how much was taken out.

There are a few things to think about with the catheter method:

It may feel uncomfortable.

It might make you more likely to get an infection.

It’s rare, but it could injure your urethra.

Ultrasound

With this method, after you pee, the nurse will hold the ultrasound wand against your belly. Pictures of your bladder will show up on a monitor, and your doctor will use them to measure the urine there.

This method has a few advantages over the catheter method.

Because nothing goes inside your body, there’s no chance of injury or infection.